Variable speed photographic process printers normally operate at either a default speed or a user selectable speed. Typically, the print speed can be configured by switch settings, a front panel menu, programmatically from the processor, or a combination of these methods. Also, a printer will typically start printing at a fixed rate when the print buffer contains more than a certain threshold of lines to print, and the printer will pause whenever it has printed all the data in the print buffer. Some prior art printers also change print speed depending on the available data lines in the print buffer. The methods for controlling these printers typically have response characteristics which vary with data resolution and frequency of receipt of new lines.
One problem with prior art printers is that if the printer responds too rapidly or it exhibits an underdamped behavior, it may leave visible blemishes or artifacts on the printed image. A risk of leaving artifacts always exists when the printer stops.
Another problem with prior art printers, particularly those printers printing at a high resolution, is a significant increase in registration problems if the printer starts and stops too frequently.
Still another problem with prior art printers is the difficulty of varying the print speed if the printer is capable of printing at various data resolutions. That is, the number of print lines printed per input data line is higher for low resolution data because multiple lines must be printed for each line of input data when printing in low resolution. Therefore, when the input data rate changes, the print rate will change more rapidly when printing lower resolution data then it changes when printing higher resolution data. If this variation in the rate of change is not controlled, the media drive system and the system that places data onto the media can lose synchronization causing blemishes or artifacts to be left on the printed media.
There is need in the art then for a printer that will vary print speed relative to the input data rate, filtering abrupt changes in host data rate and attempting to keep the print media moving by frequently adjusting print speed relative to available print lines. There is further need in the art for such a printer control system that varies the print speed relatively independent of the resolution of the data being printed. The present invention meets these needs.
A description of other aspects of the printer that incorporates the present invention can be found in application Ser. No. 07/650,690 filed Feb. 5, 1991 of Sturm, et al., entitled "CRT Beam Deflection Control System," which is specifically incorporated by reference for all that is disclosed therein.